As the development of communication technologies, various modulation manners of high spectrum efficiency are widely used. Modulation signals obtained by using various pulse-forming filters have very high frequency efficiencies; however, the amplitudes and phases of such modulation signals are variable, such variation requiring that the power amplifier in the transmitter has a linear property. Predistortion linearization technology is a common effective method, the principle of which being to make the whole system exhibiting a linear property by a predistortion device with a property contrary to the nonlinear property of the power amplifier.
FIG. 1 is a schematic diagram of digital predistortion of the prior art. As shown in FIG. 1, the signals of a transmitting circuit 101 may be fed back to a predistortion unit 103 by a predistortion feedback circuit 102, so that the predistortion unit 103 adjusts the transmission signals by using a predistortion coefficient. However, an additional feedback circuit (such as the predistortion feedback circuit 102) is needed in such a technical solution, and the feedback circuit has a high requirement on the bandwidth. For example, it requires that the feedback circuit has a very high linearity, and the bandwidth is 3 to 5 times of that of the signals of a receiving circuit, thereby resulting in very high cost.
Currently, some methods of reusing analog receiving circuit are used to solve the above problems. For example, in a time-division duplexing (TDD) communication system, a receiver circuit is used as a predistortion feedback circuit during the transmitting time. The system is switched over between a nonlinear calibration mode and a normal mode by an attenuator and a switch.
FIG. 2 is a schematic diagram of reusing an analog receiving circuit in the prior art. As shown in FIG. 2, when predistortion processing is needed, a switch 205 is used to connect an attenuator 204 and a receiving circuit 202, so that the signals of a transmitting circuit 201 are fed back to a baseband processing part 203 via the receiving circuit 202; and when signals are needed to be received, the switch 205 switches off the attenuator 204 and receiving circuit 202, so that the receiving circuit 202 receives signals from an antenna, thereby realizing normal signal receiving. In this way, the receiving circuit 202 may be used to feed distortion signals back to the baseband processing part 203, so as to realize predistortion processing, with no need of an additional predistortion feedback circuit.
However, in the implementation of the present invention, this applicant found that there exist defects in the above reusing technology: it is only applicable to a half duplexing system, such as time division duplexing (TDD), but is not applicable to a full duplexing system, such as frequency division duplexing (FDD). And even a half duplexing system has a very high requirement on the analog receiving circuit, thereby resulting in very high cost.